JOINT MOMENTS AND NEUROMUSCULAR FUNCTIONING IN DROP JUMP EXERCISES

INTRODUCTION: Drop jump (DJ) exercises from different dropping heights are often used to obtain important data about the degree of adaptability of the locomotor system to increasing amounts of mechanical load. The purpose of this study was to analyze the adaptation of the neuromuscular system to mechanical load increases. These neuromuscular adaptations where related to the joints’ moments of force and to relative changes in the length of the leg extensor muscles. METHODS: Ten elite sprinters (height: 182±5.0 cm, body mass: 75.3±4.5 kg, best performance over 100 meters: 10.4±0.2 s) performed 6 DJs from 25, 40, 55 and 70 cm. EMG signals and ground reaction forces were recorded at 1000 Hz. EMGs from the tibialis anterior (TA), soleus (SOL), gastrocnemius (GAS), rectus femoris (RF), vastus medialis (VM), biceps femoris (BF) and gluteus maximus GM muscles were full wave rectified and integrated (iEMG) across different functional phases: pre-activation (PRE) (100 ms prior to contact), reflex induced activation phase (RIA) (from 20 ms to 100 ms after contact) and late EMG response phase (LER) (from 100 ms to the finish). Vertical peak and vertical net impulses were calculated. Simultaneously, angular kinematic data on the ankle, knee and hip joints were calculated using a video analysis system (120 Hz). Joint net moments from the hip, knee and ankle were calculated using an inverse dynamics method. Student’s T-tests were used to analyze the effects of drop jump height. RESULTS: The stretching and shortening velocities increased in all muscles with an increase in DJ height. Nevertheless, no differences were found in vertical jumping performance between DJs executed from different heights. The subjects were able to reduce the increasing stretching load, producing higher vertical net impulses during the downward movement. The percentage of total length changes of GAS, RF, VM and SOL increased with stretching load, average values increasing from 4.7% at DJ25 to 7.8% at DJ70; these values are inside the short range elastic stiffness. The iEMG of the RIA phase increased slightly with the increase of dropping height for VM, RF, GAS, SOL. For these muscles, the RIA phase presented higher iEMG values when compared with LER. For the four jumping heights, the peak values of hip, knee and ankle joint moments were similar. Nevertheless, a different joint moment/time curve pattern was obtained. On DJ70, the peak values of joint moments of the three joints were obtained earlier, coinciding with the stretching phase of the muscles studied. For DJ70, a decline in the value of the moments of force on the three joints was observed during the ascending phase. CONCLUSION: The athletes studied were able to resist increasing stretching speeds and forces during the braking phase. This ability was related to the increased capability of maintaining high levels of stretch reflex during the RIA phase, revealing the importance of the stretch reflex effect on increasing muscle stiffness

DROP JUMP TRAINING STIMULUS INDUCES DIFFERENT QUALITATIVE ADAPTATIONS ON THE ELECTROMYOGRAPHIC (EMG) PATTERN OF THE LEG EXTENSOR MUSCLES

INTRODUCTION Jumping technique can dramatically affect drop jump performance (Warren et al., 1995), which suggests that the quality of the training stimulus may also influence the neuromuscular control of drop jump exercises. The present study was designed to investigate the changes in performance characteristics and in neuronal activation patterns, induced by different drop jump training stimulus. Thirteen healthy males were involved in an 8 weeks training program, followed by a detraining period o 4 weeks and a new training period of 4 additional weeks. The subjects exercised 3 to 4 times per week. They performed reactive.DJ from their best drop height. All the training sessions were supervised. During the sessions of the first 4 weeks the subjects were informed on the flight time of each jump and a reactive jump with maximal effort with a short contact time were continuously demanded by the supervisor. On the training sessions from week 4 to week 8 the supervisor only informed the subjects about the flight time of the jump. Finally, on the last 4 weeks the subjects were informed both on the flight and contact time of each jump. The testing procedures took place before and after each 4 weeks. The subjects performed reactive drop jump (DJ) exercises from the heights of 25, 40, 55 and 70 cm. The vertical ground reaction forces and the surface electromyograms (EMG) of the triceps surae muscles (GAS and SOL) were recorded. The EMGs were full-wave rectified and integrated (iEMG) over different functional phases (Schmidtbleicher et al., 1988): Preactivation phase (PRE) (100ms before ground contact); Reflex Induced Activation phase (i.e. the activation phase from 40 ms to 120 ms after impact); Late EMG Response phase (LER) (activity from 120 ms until the end of contact). RESULTS Table 1 summarises the results observed on the jump heightlcontact time ratio (JHCT) during the training process. Table 1- Mean and standard deviation of the jump height contacV contact time ratio (JHICT), for drop jump exercises from 25 cm (DJ25), 40 cm (DJ40), 55 cm (DJ55) and 70 cm (DJ70), during the training The increase on the jump height/contact time ratio (JHCT) corresponds to the training periods where the subjects were continuously instructed to jump reactively and received feedback information on the jump height and contact time of each individual drop jump. A decrease on the jump height/contact time ratio (JHCT) occurred when the feedback was only the jump height of the drop jumps. The EMG results showed a qualitative shifting in the EMG-patterns toward an accented RIA-phase activation, when the JHCT ratio increased. Additionally the changes in contact time were correlated negatively (r=-0.70 ; -0.85, pc0.001) with the iEMG of the RIA-phase for GAS and SOL muscles. CONCLUSION These results revealed that feedback on the jumping performance, produced clear differences on the biomechanics of the jump. Qualitative adaptations on the EMG pattern induced by a strength training program with drop jump exercises, are only observed if the jumping technique allows for a good jump height/contact time ratio. These parameter should be used to monitor the quality of reactive strength training stimulus

JOINT MOMENTS AND NEUROMUSCULAR FUNCTIONING IN DROP JUMP EXERCISES

INTRODUCTION: Drop jump (DJ) exercises from different dropping heights are often used to obtain important data about the degree of adaptability of the locomotor system to increasing amounts of mechanical load. The purpose of this study was to analyze the adaptation of the neuromuscular system to mechanical load increases. These neuromuscular adaptations where related to the joints’ moments of force and to relative changes in the length of the leg extensor muscles. METHODS: Ten elite sprinters (height: 182±5.0 cm, body mass: 75.3±4.5 kg, best performance over 100 meters: 10.4±0.2 s) performed 6 DJs from 25, 40, 55 and 70 cm. EMG signals and ground reaction forces were recorded at 1000 Hz. EMGs from the tibialis anterior (TA), soleus (SOL), gastrocnemius (GAS), rectus femoris (RF), vastus medialis (VM), biceps femoris (BF) and gluteus maximus GM muscles were full wave rectified and integrated (iEMG) across different functional phases: pre-activation (PRE) (100 ms prior to contact), reflex induced activation phase (RIA) (from 20 ms to 100 ms after contact) and late EMG response phase (LER) (from 100 ms to the finish). Vertical peak and vertical net impulses were calculated. Simultaneously, angular kinematic data on the ankle, knee and hip joints were calculated using a video analysis system (120 Hz). Joint net moments from the hip, knee and ankle were calculated using an inverse dynamics method. Student’s T-tests were used to analyze the effects of drop jump height. RESULTS: The stretching and shortening velocities increased in all muscles with an increase in DJ height. Nevertheless, no differences were found in vertical jumping performance between DJs executed from different heights. The subjects were able to reduce the increasing stretching load, producing higher vertical net impulses during the downward movement. The percentage of total length changes of GAS, RF, VM and SOL increased with stretching load, average values increasing from 4.7% at DJ25 to 7.8% at DJ70; these values are inside the short range elastic stiffness. The iEMG of the RIA phase increased slightly with the increase of dropping height for VM, RF, GAS, SOL. For these muscles, the RIA phase presented higher iEMG values when compared with LER. For the four jumping heights, the peak values of hip, knee and ankle joint moments were similar. Nevertheless, a different joint moment/time curve pattern was obtained. On DJ70, the peak values of joint moments of the three joints were obtained earlier, coinciding with the stretching phase of the muscles studied. For DJ70, a decline in the value of the moments of force on the three joints was observed during the ascending phase. CONCLUSION: The athletes studied were able to resist increasing stretching speeds and forces during the braking phase. This ability was related to the increased capability of maintaining high levels of stretch reflex during the RIA phase, revealing the importance of the stretch reflex effect on increasing muscle stiffness

CINEMATIC ANALYSIS OF THE ANKLE AND SUBTALAR JOINTS RELATED TO MYOELECTMC ACTIVATION PATTERNS IN JUMPING EXERCISES UNDER INCREASE STRETCHING LOADS

The study of the Rear foot mobility around the subtalar joint during running and jumping exercises, has been done since 1978. In epidemiological studies the amount of eversion (pronation) is often related to injuries on the mediolateral muscles an also to Tibialis and Achilles tendons injuries. Same experiments have been made to study the rearfoot mobility considering the action of muscles located around the subtalar and ankle joints. Stacoff et al. (1988) used one mechanical model that included mediolateral muscles, the maximal force of each muscles was considered to be function of is cross sectional area. Studies that integrate both, the cinematic analysis of the rearfoot mobility around the subtalar joint and the determination of EMG activation patterns of the muscles acting on the subtalar joints are uncommon. The purpose of this work is to study the EMG patterns of same of the leg muscles involved in ankle and subtalar movements, during action against the ground, in jumping exercises under increase stretching load, looking for possible relations with the cinematic analysis of subtalar movement during ground contact phase. Five adult elite sprinters performed drop jumps under three load conditions 40cm, 50cm and 70cm. On condition five trials were recorded allowing the use of average techniques. The signals from Force Plate, Knee and Ankle electrogoniometers, and surface EMG, were A/D converted at IOOOHz (Biopac-MP100). The EMGs of Gastrocnemius (GN), Soleus (SOL), Tibialis A. (TA) and Peronis L. (PL) were filtered, fullwave rectified and smoothed. The subjects foot and leg were filmed from behind at 50 framesls. The EMG patterns of extensor muscles under SSC conditions have three functional phases, Preactivation (before touchdown (TD), Reflexive Potenciation 30-100 ms after TD and Voluntary Activation, iEMGs of this phases were calculated. PL SOL and GN act almost simultaneously during ground contact, the a higher preactivation on the GN, could be explained by the higher rate of FastT. fibbers, greater crossectional area and is superficial position. The high level of preactivation on TA appears to be related with anticipation of the forced eversion occurring after touchdown, notice that TA works as extension antagonist. This amount of activation of TA on Touchdown could explain same of the stress related TA tendon injuries

Kinematic and electromyographic analyses of a karate punch

The aims of this study were: (i) to present the kinematic and electromyographic patterns of the choku-zuki punch performed by 18 experienced karatekas from the Portuguese team, and (ii) to compare it with the execution of 19 participants without any karate experience. The kinematic and electromyographic data were collected from the arm and forearm during the execution of the specific punch. A two-way analysis of variance (ANOVA) was used with significant level set at p</=0.05. We found that the kinematic and neuromuscular activity in this punch occurs within 400ms. Muscle activities and kinematic analysis presented a sequence of activation bracing a near-distal end, with the arm muscles showing greater intensity of activation than muscles in the forearm. In the skill performance, the arm, flexion and internal rotation, and the forearm extension and pronation movements were executed with smaller amplitude in the karate group. Based on the results of this study, the two groups' presented distinct kinematic and electromyographic patterns during the performance of the choku-zuki punch

Fatigue Evaluation through Machine Learning and a Global Fatigue Descriptor

Research in physiology and sports science has shown that fatigue, a complex psychophysiological phenomenon, has a relevant impact in performance and in the correct functioning of our motricity system, potentially being a cause of damage to the human organism. Fatigue can be seen as a subjective or objective phenomenon. Subjective fatigue corresponds to a mental and cognitive event, while fatigue referred as objective is a physical phenomenon. Despite the fact that subjective fatigue is often undervalued, only a physically and mentally healthy athlete is able to achieve top performance in a discipline. )erefore, we argue that physical training programs should address the preventive assessment of both subjective and objective fatigue mechanisms in order to minimize the risk of injuries. In this context, our paper presents a machine-learning system capable of extracting individual fatigue descriptors (IFDs) from electromyographic (EMG) and heart rate variability (HRV) measurements. Our novel approach, using two types of biosignals so that a global (mental and physical) fatigue assessment is taken into account, reflects the onset of fatigue by implementing a combination of a dimensionless (0-1) global fatigue descriptor (GFD) and a support vector machine (SVM) classifier. )e system, based on 9 main combined features, achieves fatigue regime classification performances of 0.82 ± 0.24, ensuring a successful preventive assessment when dangerous fatigue levels are reached. Training data were acquired in a constant work rate test (executed by 14 subjects using a cycloergometry device), where the variable under study (fatigue) gradually increased until the volunteer reached an objective exhaustion state

Non-invasive assessment of sciatic nerve stiffness during human ankle motion using ultrasound shear wave elastography

Peripheral nerves are exposed to mechanical stress during movement. However the in vivo mechanical properties of nerves remain largely unexplored. The primary aim of this study was to characterize the effect of passive dorsiflexion on sciatic nerve shear wave velocity (an index of stiffness) when the knee was in 90° flexion (knee 90°) or extended (knee 180°). The secondary aim was to determine the effect of five repeated dorsiflexions on the nerve shear wave velocity. Nine healthy participants were tested. The repeatability of sciatic nerve shear wave velocity was good for both knee 90° and knee 180° (ICCs≥0.92, CVs≤8.1%). The shear wave velocity of the sciatic nerve significantly increased (p<0.0001) during dorsiflexion when the knee was extended (knee 180°), but no changes were observed when the knee was flexed (90°). The shear wave velocity-angle relationship displayed a hysteresis for knee 180°. Although there was a tendency for the nerve shear wave velocity to decrease throughout the repetition of the five ankle dorsiflexions, the level of significance was not reached (p=0.055). These results demonstrate that the sciatic nerve stiffness can be non-invasively assessed during passive movements. In addition, the results highlight the importance of considering both the knee and the ankle position for clinical and biomechanical assessment of the sciatic nerve. This non-invasive technique offers new perspectives to provide new insights into nerve mechanics in both healthy and clinical populations (e.g., specific peripheral neuropathies)

Synchronization performance affects gait variability measures during cued walking

Background Incorporating variability within gait rehabilitation offers a promising approach to restore functional capacity. However, it’s success requires adequate synchronization, a parameter that lacks report in most of the literature regarding cued gait training. Research question How changes to synchronization performance during fractal-like and isochronous cueing impacts gait variability measures? Methods We asked twelve young male participants to walk in synchronization to two different temporally structure cueing (isochronous [ISO] and fractal [FRC]). We have also manipulated the cueing’s tempo by increasing and decreasing it by 5% to manipulate synchronization, resulting in six conditions (stimuli [ISO,FRC] x tempo [SLOW, NORMAL, FAST]). The normal condition was set from an uncued trial through the participant’s self-paced stride time. Synchronization performance (ASYNC) and gait variability (fractal scaling and coefficient of variation) were calculated from stride time data ( -ISIs,CV-ISIs). Repeated measures analysis of variance or Aligned Rank Transform were conducted to determine significant differences between metronome tempo and stimuli for the dependent variables Results Our results showed a FAST tempo decreases synchronization performance (ASYNC) and leads to lower -ISIs, for both ISO and FRC stimuli. This indicates that when an individual exhibits poor synchronization during cued gait training, his/her gait variability patterns will not follow the temporal structure of the presented metronome. Specifically, if the individual poorly synchronizes to the cues, the gait patterns become more random, a condition typically observed in older adults and neurological patients, which runs contrary to the hypothesis when using fractal-like metronomes. Significance This study provides supporting evidence that measuring synchronization performance in cued training is fundamental for a proper clinical interpretation of its effects. This is particularly relevant for the recent and ongoing clinical research using fractal-like metronomes since the expected gait patterns are dependent on the synchronization performance. Randomized control trials must incorporate synchronization performance related measures

Effects of a sensory strategy in an isometric muscular endurance task

AbstractObjetiveThe use of music and video in exercise domain might act in parallel over other physiological signals and its central interpretation may change the rate of perceived exertion and subsequently the final performance.The purpose of this study was to examine the effects of sensorial modulation in an isometric muscular endurance task.MethodTen volunteers have performed three tests, in which they had to keep the dominant arm abduction until exhaustion whilst the following variables: total time, rate of perceived exertion (RPE),median frequency (MF) and root mean square (RMS) were monitored. Each subject has performed a control (CO), deprivation (DP) and stimuli (SC) condition. Analysis of variance (ANOVA) one-way was applied followed by post-hoc Scheffé test. The smallest worthwhile change was used to provide a qualitative analysis of performance.ResultsNo significant differences were found in muscular activity between conditions and performance (p>0.05). The slope of RPE was significant higher to DP compared to SC (4.3 + 0.77 a.u. vs 3.53 + 0.46 a.u., p<0.05; respectively). Furthermore, a higher probability of improvement for time to exhaustion was found to SC compared to DP (97 %) and CO (92 %), conversely the opposite outcome was demonstrated to DP compared to CO (59 %).ConclusionIt was concluded that a sensory strategy was capable to modulate RPE and performance

Electromyographic Response Of The Abdominal Muscles During Curl-up Exercises With Different Loads

Aim. The present study focuses on the behavior of the abdominal muscles when performing curl-ups with loads gauged in relation to a maximum load test (1 RM). Methods. Thirteen subjects performed curl-up exercises with loads equivalent to 80, 60, 40 and 20% of the 1 RM (100%) maximum, with 5-minute rests between sets. Surface bipolar EMG electrodes were placed on the right and left Rectus Abdominis and the Obliquus Externus muscle. Differences between loads and repetitions were determined using the Shapiro-Wilk, ANOVA (Friedman) and Wilcoxon tests (P<0.05). Results. The root mean square (RMS) of the EMG was calculated for the first four and the last three repetitions. The percentage values for the abdominal muscles studied were then averaged and the result was used to represent abdominal synergy (AbSyn). Conclusion. 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